RESUMO
The ability of viable M. leprae to hydrolyze Fluorescein diacetate and retain fluorescein inside the bacteria was used to identify viable M. leprae inside the cultured in vitro macrophages. The subjective microscopic count of the FDA test was demonstrated as useful routine test by confirming the results obtained therein with a quantitative and non subjective measurement of fluorescence in spectrofluorimeter. Using this method loss of viability of M. leprae in presence of dapsone and rifampicin was demonstrated. Such an assay, was well correlated with another in vitro assay, the Fc receptor test and also the in vivo mouse foot test. The drug resistance of clinical isolates of M. leprae demonstrated by mouse foot pad was also correlated with FDA test system. Thus we have reported a reliable, consistent and rapid in vitro test system for determining viability and drug sensitivity of M. leprae.